The kids stopped because they are tired and scared of running. Vergo attempts to kill Law even though he is cut down. The Straw Hats convinced the children to run and they continue to escape the poison gas. Caesar tells his subordinates to release the poison gas into building R-66. Caesar consumes the gas and becomes a big monster. He then consumes his subordinates to intimidate Luffy. Usopp tells Caesar's subordinates that Luffy will never betray his crew. Luffy defeats Caesar with Grizzly Magnum and sends him flying away. (thetvdb.com)